After remaining beyond the margins of Home Plate ever since exiting its northeast edge on Sol 774 (March 7, 2006) to survive the first winter on Mars, Spirit finally climbed on top of the elevated, circular plateau that scientists believe is volcanic in origin.

Before completing the final drive, however, Spirit returned to the soil patch nicknamed "Gertude Weise," made of nearly pure silicon dioxide, to acquire data that will help scientists characterize how much dust has accumulated on the instrument optics of the miniature thermal emission spectrometer.

The miniature thermal emission spectrometer is inside the boxy body of the rover, below the mast. Mirrors inside the mast allow the instrument to see outside. The rover has been using the spectrometer to measure changes in the atmosphere during the recent dust storm on Mars. When the instrument is not in use, a cover protects it from dust floating in the atmosphere but it isn't air-tight.

After completing measurements of Gertrude Weise, Spirit was once again on the move. The rover attempted to "thread the needle" by driving between two rocks on sol 1304 (Sept. 3, 2007) and place the rear two wheels on the top of Home Plate (Spirit must drive backward to drag the frozen right front wheel).

As it turned out, the drive was more difficult than anticipated. On the first attempt, Spirit immediately stopped driving when the rover's wheels entered an area designated as a keepout zone. This occurred as the rover was attempting to compensate for drag from the right front wheel by turning slightly in the opposite direction. Normally, the dragging wheel causes Spirit to yaw counter-clockwise (as viewed from above), but the amount of counter-clockwise spin depends on the amount of drag encountered by the right front wheel. Rocky surfaces cause less drag than soil. In this case, the drag was less than anticipated.

On sol 1306 (Sept. 5, 2007), Spirit tried again and executed the drive flawlessly! Now that the rover's two rear wheels are on top of the eastern edge of Home Plate, Spirit is in position to explore the top of the elevated plateau along its eastern and southern edges. The next planned stop is a few meters away in an area known as "Site 2," located midway along the eastern scarp of Home Plate east scarp and several meters to the west of the scarp. (If you compared the roughly circular shape of the top of Home Plate to a clock, Site 2 would be at 3:30.)

After that, scientists plan to have Spirit proceed to "Site 3," at the southern end of Home Plate (6 o'clock position) and "Site 4," at the southwestern corner of Home Plate (7:30 position).

By collecting data at all these sites, scientists hope to interpret the geologic structure of Home Plate, determine how the rock chemistry changes from one side to the other, and elucidate a fracture that crosses the plateau from west to east. Along the way, the rover will take images of the south face of "Husband Hill" to the north and outcrops known as "Goddard" and "von Braun" to the south.

In recent months, rover handlers have been naming local features and targets around Home Plate for deceased members of the All-American Girls Professional Baseball League. Because Home Plate is bowl-shaped, scientists have decided to name features on top of Home Plate after things served in bowls. Stay tuned for upcoming yummy descriptions!

Sol-by-sol summary:

In addition to measuring atmospheric opacity with the panoramic and navigation cameras, surveying the sky and ground with the miniature thermal emission spectrometer, and checking for drift (changes with time) in the miniature thermal emission spectrometer, Spirit completed the following activities:

Sol 1303 (Sept. 2, 2007): Spirit studied a target known as "Gertrude Weise14," the background of the target, a soil target labeled "Innocent Bystander Disturbed Area 1," and a target known as "Mary Dailey3" as well as its background with the miniature thermal emission spectrometer. Spirit recalibrated the panoramic camera and acquired miniature thermal emission spectrometer data on a target dubbed "Joanne Winter2."

Sol 1304: Spirit acquired full-color images of the disturbed soil area using all 13 filters of the panoramic camera before driving 2.42 meters (7.94 feet) toward Home Plate. The rover took images just before and after completing the drive with the hazard avoidance cameras as well as post-drive images with the navigation and panoramic cameras.

Sol 1306: Before beginning the sol's drive, Spirit acquired full-color images of the rover's external calibration target as well as the disturbed soil area of Innocent Bystander using all 13 filters of the panoramic camera. After completing the 8.21-meter (26.9-foot) drive, the rover took images of the surrounding terrain with the navigation camera and forward-looking images with the panoramic camera.

Sol 1307: Spirit completed a survey of rock clasts with the panoramic camera and assessed the calibration target with the miniature thermal emission spectrometer.

Sol 1308 (Sept. 7, 2007): Spirit acquired images of dust in the sky with the panoramic camera, calibrated the miniature thermal emission spectrometer, and listed files in the rover's flash memory (a type of rewritable electronic memory that retains information even when power is off). Spirit completed a systematic foreground survey using all 13 filters of the panoramic camera and measured albedo (surface reflectivity) using the panoramic camera. With the miniature thermal emission spectrometer, the rover surveyed a soil target known as "Beef_Chili," a rock target known as "Cajun_Chili," and the external calibration target.

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